In production line operations in various industries there is the need to apply colored inks, paints, and the like, for marking purposes, where it is of prime importance that the minimum of time elapse when changing from one color to another. The color being used is intended mainly for identification purposes, and the fact that a color may be somewhat off-shade is not critical, as long as it can be recognized.
A typical example is the application of ink to the outside of insulated wire. A wire with a white colored insulation may have applied to it various colored markings so that it can be identified for ease in wiring and troubleshooting purposes. Some wire may be marked with red dots or lines, some with blue, some with blue and red, etc. One practice in marking such wire, is to apply ink from a rotating nozzle or wheel-type applicator which throws ink on the wire as it passes through an enclosure. This ink is applied from a pressure container or pump, and discharged to atmosphere in proximity to the wire, with ink which does not adhere to the wire being reclaimed and re-circulated to the supply tank, saved for future use, or discarded.
If a red ink is being applied and the time arrives where it is required to switch to a new color ink, the operator must cut off the supply of red ink, use a solvent to purge the red ink remaining in the system to insure that there will not be sufficient residue of the red ink left to influence the new color to the point where it would not be readily recognized, and then connect the new color to the system and start running. This is a time-consuming process requiring many minutes for the skillful operator and sometimes, without the assurance that adequate cleaning has been achieved. During this color changeover time, the wire may have been running at 5,000 feet per minute, and indiscriminate marking would have been applied while the color change was in progress. This wire, in many cases, would have to be discarded or used as seconds. Furthermore, there is a time-consuming requirement insofar that the improperly marked wire must be unrolled to remove it from the production line.